Unit #4 Waste and Excretion The Kidneys
Renal Hilus (Hilus) the doorway of the kidney Ureter leaves this region blood and lymphatic vessels enter and exit here Renal Capsule (Capsule) smooth fibrous tissue that surrounds, encloses and protects the kidney helps kidney maintain its shape surrounded by fatty tissue which act as extra cushion in case of sudden movements or impacts Renal Cortex (Cortex) Outer part of the kidney contains the Bownan s Capsule, Glomeruli, and Convoluted Tubules (top ½ of the Nephrons)
Renal Medulla (Medulla) Inner part of the Kidney Contains the Loop of Henle and Collecting Tubules (bottom ½ of the Nephrons) Also contains Renal Pyramids - 5 to 18 pyramid shaped striated (striped) regions Renal Pelvis funnel shaped basin (cavity) that receives Urine drained through the collecting tubules from the Nephrons
The Nephron The Functional Units of the Kidney (where most of the work takes place) each kidney has approximately 1 million of these 2 parts each Nephron: 1. The Renal Corpuscle made up of the Glomerulus and Bowman s Capsule filters blood plasma 2. The Renal Tubules reabsorbs anything useful and removes waste
How the Nephron Works
Blood Enters the Renal Corpuscles 1. Dirty Blood flows from the Renal Artery into an Interlobular Artery and then into an Afferent Arteriole 2. Blood enters the Glomerulus the glomerulus contains a series of capillaries that are under higher than normal pressure the pressure forces Urea, Salts, Glucose and most of the water through the capillary walls separating it from the rest of the blood plasma the remaining blood plasma will flow through the Efferent Arteriole and into the capillary network that surrounds the nephron the material forced out is called Glomerular Filtrate 3. The Glomerular Filtrate is collected in the Bowman s Capsule and is then passed into the Renal Tubules
Blood Enters the Renal Tubules 4. Filtrate passes through the Proximal Convoluted Tubule in the PCT most of the water and almost all of the glucose and nutrients present in the filtrate are reabsorbed into the capillaries
5. Filtrate is passed into the Loop of Henle the Loop of Henle is Selectively Permeable the 1st part of the loop is called the Descending Limb the Descending limb is permeable to water but NOT salt or urea water moves by osmosis from surrounding tissues and capillaries into the Descending limb the 2nd part of the loop is called the Ascending Limb the Ascending Limb is NOT permeable to water but is permeable to salt salt will diffuse into the capillaries but the water and urea will stay in the limb
6. Filtrate is passed into the Distil Convoluted Tubule The Distil Convoluted Tubule is selectively permeable depending on the presence of the Anti Diuretic Hormone (ADH) if the body is properly hydrated there is a low concentration of ADH. The body does not need additional water and the DCT becomes permeable to water allowing water to move into DCT by osmosis If the body is dehydrated there is a high concentration of ADH. The body needs more water so the DCT becomes impermeable to water which prevents water from moving into the DCT
7. Clean Blood flows from the capillaries to veins and into an Interlobular Vein which carries the blood to the Renal Vein 8. the fluid leaving the DCT is now considered Urine and flows into the Collecting Ducts which empty into the minor and major calyx (calces plural) which then flow into the Renal Pelvis
The Act of Urination only 1% of the original filtrate volume is released as urine healthy urine has a ph of about 6 (the Kidney will add ions to the filtrate to maintain this ph level) Ureters carry the urine to the Urinary Bladder as the Urine volume increases so does the pressure on the Urinary Bladder and the bladder will distend (expand) As the bladder expands it put pressure on the Urinary Sphincter which triggers the urge to go Increased pressure leads to peristalsis of the bladder The Urinary Sphincter is a voluntary sphincter up to a certain point Urinary Sphincter relaxes and Urine is released through the Urethra